Electroactive polymer transducers biased for increased output

ABSTRACT

Electroactive polymer transducers are disclosed. They are biased in a manner that provides for increased force and/or stroke output, thereby offering improved work potential and power output capacity. The biasing may offer additional or alternate functional advantage in terms of matching transducer performance with a given application such as a normally-closed valve. The improved biasing (including increased output biasing) may utilize negative spring rate biasing and/or a combination of negative or zero-rate biasing with positive rate biasing to achieve the desired ends.

FIELD OF THE INVENTION

The invention is related to electroactive polymer transducers andoptimizing their performance by selectively biasing their electroactivepolymer films.

BACKGROUND OF THE INVENTION

A tremendous variety of devices used today rely on actuators of one sortor another to convert electrical energy to mechanical energy. Theactuators “give life” to these products, putting them in motion.Conversely, many power generation applications operate by convertingmechanical action into electrical energy. Employed to harvest mechanicalenergy in this fashion, the same type of actuator may be referred to asa generator. Likewise, when the structure is employed to convertphysical stimulus such as vibration or pressure into an electricalsignal for measurement purposes, it may be referred to as a transducer.Yet, the term “transducer” may be used to generically refer to any ofthe devices. By any name, a new class of components employingelectroactive polymers can be configured to serve these functions.

Especially for actuator and generator applications, a number of designconsiderations favor the selection and use of advanced electroactivepolymer technology based transducers. These considerations includepotential force, power density, power conversion/consumption, size,weight, cost, response time, duty cycle, service requirements,environmental impact, etc. Electroactive Polymer Artificial Muscle(EPAM™) technology developed by SRI International and licenseeArtificial Muscle, Inc. excels in each of these categories relative toother available technologies. In many applications, EPAM™ technologyoffers an ideal replacement for piezoelectric, shape-memory alloy (SMA)and electromagnetic (EM) devices such as motors and solenoids.

As an actuator, EPAM™ technology operates by application of a voltageacross two thin elastic film electrodes separated by an elasticdielectric polymer, such as silicone or acrylic. When a voltagedifference is applied to the electrodes, the oppositely-charged membersattract each other producing pressure upon the polymer therebetween. Thepressure pulls the electrodes together, causing the dielectric polymerfilm to become thinner (the z-axis component shrinks) as it expands inthe planar directions (the x- and y-axes of the polymer film grow).Another factor drives the thinning and expansion of the polymer film.The like (same) charge distributed across each elastic film electrodecauses the conductive particles embedded within the film to repel oneanother expanding the elastic electrodes and dielectric attached polymerfilm.

Using this “shape-shifting” technology, Artificial Muscle, Inc. isdeveloping a family of new solid-state devices for use in a wide varietyof industrial, medical, consumer, and electronics applications. Currentproduct architectures include: actuators, motors, transducers/sensors,pumps, and generators. Actuators are enabled by the action discussedabove. Generators and sensors are enabled by virtue of changingcapacitance upon physical deformation of the material.

Artificial Muscle, Inc. has introduced a number of fundamental “turnkey”type devices that can be used as building blocks to replace existingdevices. Each of the devices employs a frame structure to support theEPAM™ film whereby application of a voltage shifts the position of thedevice assembly back and forth. The film can be engaged with (e.g.,stretched by) the frame in such a way so as to pre-strain the film. Ithas been observed that pre-straining improves the dielectric strength ofthe polymer, thereby offering improvement for conversion betweenelectrical and mechanical energy by allowing higher field potentials.

By varying the frame configuration and the manner in which the EPAM™material is supported by the frame, different types of actuators can beprovided to address many types of applications. Non-limiting examples ofactuator types include linear actuators, bending beam actuators, planaractuators, diaphragm actuators, etc.

Linear actuators, often referred to as “spring roll” actuators, areprepared by wrapping layers of EPAM™ material around a helical spring.The EPAM™ material is connected to caps/covers at the ends of the springto secure its position. The body of the spring supports a radial orcircumferential pre-strain on the EPAM™ while lengthwise compression ofthe spring offers axial pre-strain. Voltage applied causes the film tosqueeze down in thickness and relax lengthwise, allowing the spring(hence, the entire device) to expand. By forming electrodes to createtwo or more individually addressed sections around the circumference,electrically activating one such section causes the roll to extend andthe entire structure to bend away from that side.

Bending beam actuators are formed by affixing one or more layers ofstretched EPAM™ material along the surface of a beam. As voltage isapplied, the EPAM™ material shrinks in thickness and grows in length.The growth in length along one side of the beam causes the beam to bendaway from the activated layer(s).

Another class of devices situates one or more film sections in asubstantially planar frame structure. In one variation of planar-typeactuators, the frame includes closed linkages or spring-hinges. When alinkage frame is employed, a biasing spring may generally be employed topre-strain the EPAM™ film. A spring-hinge structure may inherentlyinclude the requisite biasing. In any case, the application of voltagewill alter the frame or linkage configuration, thereby providing themechanical output desired within the planar directions defined by theframe structure.

Diaphragm actuators are similarly constructed to the above-describedplanar actuators, but provide mechanical output outside the physicalplane of the frame structure. In many embodiments, diaphragm actuatorsare made by stretching EPAM™ film over an opening in a rigid frame.Diaphragm actuators can displace volume, making them suitable for use aspumps or loudspeakers, etc.

More complex actuators can also be constructed. “Inch-worm” and rotaryoutput type devices are examples of such. Further description anddetails regarding the above-referenced devices as well as others may befound in the following patents, patent application publications and/orcurrently unpublished patent applications:

-   -   U.S. Pat. No. 7,064,472 Electroactive Polymer Devices for Moving        Fluid    -   U.S. Pat. No. 7,052,594 Devices and Methods for Controlling        Fluid Flow Using Elastic Sheet Deflection    -   U.S. Pat. No. 7,049,732 Electroactive Polymers    -   U.S. Pat. No. 7,034,432 Electroactive Polymer Generators    -   U.S. Pat. No. 6,940,221 Electroactive Polymer Transducers and        Actuators    -   U.S. Pat. No. 6,911,764 Energy Efficient Electroactive Polymers        and Electroactive Polymer Devices    -   U.S. Pat. No. 6,891,317 Rolled Electroactive Polymers    -   U.S. Pat. No. 6,882,086 Variable Stiffness Electroactive Polymer        Systems    -   U.S. Pat. No. 6,876,135 Master/slave Electroactive Polymer        Systems    -   U.S. Pat. No. 6,812,624 Electroactive polymers    -   U.S. Pat. No. 6,809,462 Electroactive polymer sensors    -   U.S. Pat. No. 6,806,621 Electroactive polymer rotary motors    -   U.S. Pat. No. 6,781,284 Electroactive polymer transducers and        actuators    -   U.S. Pat. No. 6,768,246 Biologically powered electroactive        polymer generators    -   U.S. Pat. No. 6,707,236 Non-contact electroactive polymer        electrodes    -   U.S. Pat. No. 6,664,718 Monolithic electroactive polymers    -   U.S. Pat. No. 6,628,040 Electroactive polymer thermal electric        generators    -   U.S. Pat. No. 6,586,859 Electroactive polymer animated devices    -   U.S. Pat. No. 6,583,533 Electroactive polymer electrodes    -   U.S. Pat. No. 6,545,384 Electroactive polymer devices    -   U.S. Pat. No. 6,543,110 Electroactive polymer fabrication    -   U.S. Pat. No. 6,376,971 Electroactive polymer electrodes    -   U.S. Pat. No. 6,343,129 Elastomeric dielectric polymer film        sonic actuator    -   2006/0119225 Electroactive polymer motors    -   2005/0157893 Surface deformation electroactive polymer        transducers    -   2004/0263028 Electroactive polymers    -   2004/0217671 Rolled electroactive polymers    -   2004/0124738 Electroactive polymer thermal electric generators    -   2004/0046739 Pliable device navigation method and apparatus    -   2002/0175598 Electroactive polymer rotary clutch motors    -   2002/0122561 Elastomeric dielectric polymer film sonic actuator        Each of these documents is incorporated herein by reference in        its entirety for the purpose of providing background and/or        further detail regarding underlying technology and features as        may be used in connection with or in combination with the        aspects of present invention set forth herein.

More complex frame structures have also been developed by the assigneehereof with an eye towards producing more practical and versatileactuator structures. In this regard, frustum-shaped diaphragm actuatorsare ideal. These are formed by providing a centrally disposed “cap” ordisc on the electroactive film of a standard diaphragm type-actuator andthen displacing the diaphragm/cap in a direction perpendicular to theplane defined by the frame structure. As such, the cap provides amechanical preloaded element.

The frustum diaphragm structure is highly practical and advantageous fora variety of applications, including but not limited to pumps, valves,camera lens, light reflectors, speaker diaphragms, multi-axis positionsensors/joysticks, vibrators, haptic or force feedback control devices,multi-axis actuators, etc. These frustum-type actuators or morethoroughly described in U.S. patent application Ser. Nos. 11/085,798 and11/085,804, incorporated by reference in their entirety.

Many of the above-described actuators have configurations which involvepush-pull inputs and/or outputs which are in-plane and/or out-of-planein only two-dimensions. However, more complex frame structures can beemployed to provide three-dimensional action. One such example is foundin U.S. patent application Ser. No. 11/085,798 in which a saddle-shapedactuator is used to produce a three-dimensional output. Moreparticularly, the actuator is coupled to a pair of “wings” to offer astructure having an output which substantially mimics the flapping wingsof a flying bird or bat.

Other complex actuator structures involve the coupling together or“stacking” of two or more actuators to provide two-phase output actionand/or to amplify the output for use in more robust applications. Theactuators of the resulting structure may all have the same configuration(e.g., all have diaphragm structures) or may have configurationsdifferent from each other (e.g., diaphragm and spring roll combination).With any configuration, activating opposite sides of the actuator systemmakes the assembly rigid at a neutral point. So-configured, theactuators act like the opposing bicep and triceps muscles that controlmovements of the human arm. Alternatively, two actuators arranged inseries offers the potential to double the output in a single direction.U.S. patent application Ser. Nos. 11/085,798 and 11/085,804 disclosesuch “stacked” actuators.

Biasing against the film is employed to insure that the film moves in adesired direction rather than simply wrinkle upon electrode activationthat causes the material to expand. Known biasing means include simplepositive rate springs (such as a coil spring and leaf springs), EPAM™film or non-active film set to pull against the biased material, byresilient foam, air pressure or a weight. U.S. patent application Ser.Nos. 11/085,798 and 11/085,804 disclose a number of such arrangements.

While the devices described above provide highly functional examples ofEPAM™ technology actuators/transducers, there continues to be aninterest in improving high performance EPAM™ actuators/transducers. Inparticular, it would be advantageous to improve force or stroke, workand, hence, power output without simply employing more electroactivepolymer material. The present invention is directed at making such gainsby new modes of selectively biasing the actuator film.

SUMMARY OF THE INVENTION

The electroactive polymer transducers according to the present inventionare configured to be selectively biased to obtain specifically desiredperformance characteristics. The selection of biasing according to oneaspect of the invention follows a negative bias spring model in whichthe spring force increases as the transducer's electroactive film movesfrom a preloaded position to its most highly activated position. Themodel may exclusively employ a negative bias spring, or may furtherincorporate constant force spring bias and/or a positive or “standard”spring-bias is combined with flat-rate or negative rate biasing. Thebiasing devices may additionally include biasing components of any of acoil spring, leaf spring, air or fluid pressure biasing, etc. or acombination of any of these means or the like, are also contemplatedwithin the present invention.

In addition to predictive modeling and implementation of desirablebiasing rates/profiles, the invention also includes novel springconfigurations. One such configuration comprises a “buckled” type ofbeam spring. One or more such members may be provided in a bi-stableleaf-spring arrangement. However configured, the spring operates byprogressively compressing an “S” or “C” shaped member. Another springtype comprises a polymeric (preferably molded rubber) bias diaphragm.The active spring portion of such an element may also take an “S” or “C”shaped form. The diaphragm may provide biasing, alone, or offeradditional utility as a baffle wall within a valve body, as all or aportion of a pump diaphragm surface, etc. Yet another springconfiguration suitable for negative rate biasing is provided in the formof a cartridge in which one or more compression springs are constrainedby the geometry of a linkage.

Still other implementations are possible. For example, a simply loadedbeam or leaf spring may be employed to generate a negative orsubstantially flat bias rate by virtue of material selection.Specifically, superelastic NiTi (or another superelasticmaterial—including polymers) that exhibit pseudoelastic deformation andrecovery may be employed.

The present invention further includes methodologies for selectivelybiasing an electroactive polymer transducer, methods for performingactuations and the like with the subject electroactive transducers andmethods of using the subject transducers for various applications.Without identifying each and every application in which the subjecttransducers may be employed, a non-exhaustive list includes actuators,motors, generators, pumps, valves, sensors, etc.

These and other features, objects and advantages of the invention willbecome apparent to those persons skilled in the art upon reading thedetails of the invention as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying schematic drawings. Tofacilitate understanding, the same reference numerals have been used(where practical) to designate similar elements that are common to thedrawings. Included in the drawings are the following:

FIG. 1 diagrammatically illustrates the geometry of a single-sidedfrustum-shaped transducer;

FIGS. 2A and 2B diagrammatically illustrate the geometry and function ofa double-sided frustum-shaped transducer;

FIGS. 3A and 3B diagrammatically illustrate the geometry of transducerassemblies of stacked double-sided frustum-shaped transducers in serialand parallel configurations, respectively;

FIG. 4 provides a perspective cross-sectional view of a single-sidedfrustum-shaped transducer having an EPAM diaphragm that is biased by acoil spring;

FIG. 5 provides a perspective cross-sectional view of a single cartridgestack 2-phase film biased transducer assembly having an EPAM diaphragmthat is conventionally biased;

FIG. 6 provides a perspective cross-sectional view of a seriallystacked, single phase transducer assembly having an EPAM diaphragm thatis conventionally biased;

FIG. 7 provides a perspective cross-sectional view of a parallelstacked, two-phase transducer assembly having an EPAM diaphragm that isconventionally biased;

FIG. 8 is a graph plotting the force-stroke relationships of two-phase,double-sided frustum-shaped transducer assemblies having variousstructural configurations and which are conventionally biased;

FIG. 9 provides a perspective cross-sectional view of a single-sidedfrustum-shaped transducer having an EPAM diaphragm that is biased with aconstant force (zero rate spring) mechanism;

FIG. 10 provides a perspective view of a single-sided frustum-shapedtransducer having an EPAM diaphragm that is biased with weighted mass;

FIG. 11 provides a perspective view of a single-sided frustum-shapedtransducer having an EPAM diaphragm that is biased with a leaf springmechanism;

FIG. 12 provides a view of a cut-out sheet of material for producing a“clover” type negative rate spring for use in the present invention;

FIG. 13A provides a perspective view of a single-sided frustum-shapedtransducer having an EPAM diaphragm that is biased with another type ofnegative rate spring bias mechanism comprising a multiple leaf springstructure constructed with the spring element shown in FIG. 12; FIG. 13Bshows a lateral cross-sectional view of the device of FIG. 13A takenalong the section line shown; FIG. 13C shows a lateral cross-sectionalview of a two-phase, double-sided frustum shaped transducer employingthe multiple leaf spring mechanism shown in FIG. 13B;

FIGS. 14A-14D are charts demonstrating tunability of the spring elementin FIG. 12 as employed in a configuration resembling that shown in FIGS.13B and 13C;

FIG. 15A illustrates a schematic illustration of Belville Washer modelwith a component-to-component comparison with the device of FIG. 13A;FIG. 15B diagrammatically illustrates the force and displacementvariables of the model of FIG. 15A;

FIG. 16 illustrates the superelastic (pseudoelastic) stress-strain curveof Nickel-Titanium Shape Memory Alloy (SMA) material as may be employedin a spring used in the present invention;

FIG. 17A provides a graph comparing the force-stroke relationships oftransducers having an EPAM diaphragm under positive rate spring biasingand constant force biasing, respectively; FIG. 17B is a graph showingthe force-stroke relationship for the bi-stable negative rate biasspring alone, evidencing the two stable regions; FIG. 17C is a graphcomparing the force-stroke relationships of transducers having an EPAMdiaphragm under positive rate spring biasing and negative rate springbiasing, respectively;

FIG. 18 is a bar graph comparing the maximum stroke distances of EPAMtransducers employing various types of biasing;

FIG. 19 is a graph comparing stroke capacity of EPAM transducers atvarious operating voltages;

FIG. 20 is a graph comparing electric field values for EPAM transducersunder positive and negative biasing, respectively, at the same operatingvoltage;

FIG. 21 is a graph illustrating the force-stroke relationship forvarious EPAM transducers biased by a clover leaf type negative biasingmechanisms having varying leaf lengths and positioned at varying anglesrelative to the frame surface;

FIG. 22 illustrates the force-stroke relationship for an EPAM transducerhaving biasing mechanism exhibiting a combination of a positive biasrate and a negative rate bias to yield a combined bias rate;

FIG. 23 is a perspective view of a linkage bias cartridge assemblyemployed in the transducer shown in FIG. 26;

FIGS. 24A and 24B are top views of a device as shown in FIG. 23 havingvaried configurations, each selected to tune the biased cartridgeassembly to a desired spring rate;

FIG. 25A illustrates the exemplary performance of a cartridge springassembly as shown in its various stages of 2-phase actuation in FIG.25B; FIG. 25B illustrates various stages of 2-phase actuation of thebiased cartridge assembly of FIG. 23;

FIG. 26 is an assembly view of a double-frustum EPAM transducerincorporating a negative rate bias cartridge;

FIG. 27 illustrates the comparative performance of an EPAM transducerassembly as shown in FIG. 26 with one as shown in FIG. 5;

FIG. 28A is a perspective view of a “planar” type linear transducerincluding another type of negative spring rate assembly according to thepresent invention; FIG. 28B is an exploded view of the transducer ofFIG. 28A;

FIG. 29A-C illustrates the bias assembly shown in FIGS. 28A and 28B inthree stages of 2-phase actuation;

FIGS. 30A-30C illustrate fluidic valve applications of the transducersof the present invention, each biased in a different manner;

FIG. 31 illustrates a fluidic pump transducer biased in the manner ofthe valve transducer in FIG. 30C;

FIG. 32 is a chart showing the performance of a molded diaphragmnegative spring;

FIG. 33 is graph illustrating the force-stroke relationship of atransducer pump mechanism of the present invention, such as that shownin FIG. 31, employing a molded diaphragm negative spring;

FIG. 34 shows a lens positioner/focus assembly employing a transducerbiased by a negative rate molded spring element; and

FIG. 35 illustrates the relative stroke performance of a device as shownin FIG. 34, as compared to one employing coil spring biasing.

Variation of the invention from that shown in the figures iscontemplated.

DETAILED DESCRIPTION OF THE INVENTION

The devices, systems and methods of the present invention are nowdescribed in detail with reference to the accompanying figures. Whilethe subject electroactive polymer transducers may have any suitableconstruct, for purposes of this description, frustum-shaped transducersare particularly described and illustrated; however, those skilled inthe art will recognize other architectures suitable for use with thepresent invention. The transducers described, as well as such others asnoted above may be incorporated in the biasing approaches taught by thepresent invention. In other words, the present invention includes, butis not limited to, known EPAM architectures with the addition of biasingas described below. The present invention further contemplates the useof known electroactive polymer architectures together with biasingcomponents as described herein.

The frustum architecture of the subject EPAM™ transducers yieldsimproved output as compared to a strictly flat or planar architecture.Not to be bound by a particular theory, but it is believed that thisresult stems from use of a substantial portion or nearly all of theavailable EPAM™ diaphragm material expansion that occurs upon activationof the transducer. Stated otherwise, this type of transducer derives itsz-axis output from both the x and y components of film expansion.

FIGS. 1-3 diagrammatically illustrate the “frustum” shape of thetransducers of the present invention. In a simplified two dimensionalmodel, as shown in FIG. 1, a frustum-shape is defined by a truncatedconical or pyramid-like body or structure 10, whose top or narrow end 14(in phantom) (relative to an opposite broader end 16 defining areference plane) has been removed to define a flat surface 12. Thismodel profiles a “single-sided” transducer structure while FIGS. 2A, 2B,3A and 3B profile “double-sided” transducer structures, where the latterare formed by “stacking” together two or more single-sided and/ordouble-sided structures. Various examples of each of thesefrustum-shaped transducers are now described.

FIG. 4 illustrates a perspective cross-sectional view of a single-sidedfrustum-shaped transducer 20 having an EPAM™ diaphragm or film 24 heldby a frame 22 (having a square outer profile, for example) with, acapping structure 26 affixed or positioned centrally to the diaphragm. Abaffle wall 25 associated with the frame 22 (or part of the frameitself) whereby film 24 is sandwiched therebetween in a stretched ortensioned condition. Similarly, cap 26 may be comprised of two opposingsides which sandwich diaphragm 22 therebetween. Alternatively, thecapping structure may comprise a portion of the diaphragm which is madesubstantially more rigid through thermal, mechanical or chemicaltechniques (e.g., vulcanizing).

Generally, the capping section of the transducers of the presentinvention will be sized to produce a perimeter of sufficientdimension/length to adequately distribute stress applied to thematerial. The ratio of the size of the cap to the diameter of the frameholding the EPAM™ layers may vary. The size of the cap will be largerunder higher stress/force application. The degree of truncation of thestructure is of further importance, particularly where the aggregatevolume or space that the transducer occupies is required to be as smallas possible.

Depending on the application, desirable cross-sectional geometries ofcapping structures usable with the present invention includedisc-shaped, circular, triangular, square, pentagonal, hexagonal, etc.Often, symmetrically shaped end or cap members will be desirable fromthe perspective of consistent material performance. However, ovaloid,oblong, rectangular or other shapes may prove better for a givenapplication—especially those that are space-constrained. Furthervariation is contemplated in that the truncated or capped ends need notbe flat or planer. Additionally, in certain applications, a point-loadeddiaphragm forming a coned-shaped structure or a pressure-biased dome,etc., may be used. These structural features/physical characteristicsmay have particular significance where the capping surface or diaphragmelement is designed to serve as an active component (such as a valveseat, etc.).

Referring again to FIG. 4, when cap 26 is biased or pre-loaded in adirection (identified by arrow 18 in FIG. 1) perpendicular to the planedefined by the cap/frame, film 22 is stretched out of the plane, therebyproviding the profile illustrated in FIG. 1. Here, capping structure 26is preloaded or biased by a coil spring 28 interposed between frame 22and baffle wall 25. Coil spring 28 exhibits a positive rate springeffect against cap 26. Namely, spring force against the cappingstructure is substantially as represented by F=k(x), where F representsforce, x represents spring displacement, and k is the rate of thespring.

As discussed above, when the electroactive polymer is energized, itexpands. This allows the preloaded spring to relax to deliveryactuator/transducer stroke. Upon lowering (or terminating) voltageapplication, the electroactive polymer recovers to compress the springuntil the opposing forces equilibrate. The overall actuator is, thus, inits most stable position when activated, whereas the spring itself isstable in its uncompressed position.

In double-sided frustum transducers, two or more transducers are coupledtogether to form a transducer assembly. In the most basic ofdouble-frustum transducers, i.e., as illustrated in the profile model ofFIGS. 2A and 2B, two transducers 10 a, 10 b are stacked with theircapped surfaces held together under tension to produce concave formsfacing opposite or away from one another where one side of thetransducer assembly typically provides preload to the other.

FIG. 5 illustrates a transducer assembly 30 having the profileillustrated in FIGS. 2A and 2B. Here, a body frame 44 is employed towhich each of the two transducer frames 32, 34 are mounted by way of nutand bolt members 50. The respective transducer capping structures 36, 38are secured to one another, such as by a nut and bolt assembly, along aninterface section 48. The interface section 48 may offer a relativelystiffer or less flexible capping region than that which is possible withsingle-sided transducers.

Transducer assembly 30 operates as shown in FIG. 2B. With the cap orinterface section 12 defining a stable top/bottom surface, the attachedEPAM™ diaphragms 10 a, 10 b of the structure assume an angle withrespect to the frame or reference plane 16. When the assembly (or atransducer side) is inactive, the angle α that each diaphragm forms withits respective frame or reference plane 16 may range between about 15and about 85 degrees. More typically it will range from about 30 toabout 60 degrees. When a transducer side/diaphragm 10 b is energized, itrelaxes and pulls with less force, allowing elastic recovery of theother transducer side/diaphragm 10 a, thereby producing work throughforce and stroke of the device. Such action, indicated by the dashedline in FIG. 2B, increases the depth of one cavity while decreasing thatof the other. When voltage is applied so that the EPAM™ material iscompressed and grows in its planar dimensions, it assumes a second angleβ from about 5 to about 15 degrees greater than angle α. Optimum angleranges will vary based on application specifications.

The double-sided transducer assemblies may be configured where one orboth of the transducer sides 10 a/10 b are active. With just one activeside, i.e., a single-phase transducer, forced motion is limited to oneside of the neutral position, with the inactive side functioning assolely as a preload for the other (simply offering a replacement forcoil spring 28 in the first referenced embodiment). Where bothdiaphragms comprise EPAM™ film, i.e., a double-phase transducer, thenthe actuator can move in/out or up/down relative to a neutral position,as indicated by double-headed arrow 15. In the latter configuration,each side may act as a preload or bias for the other with or withoutother means of biasing/preload. Whether the double-sided transducersassemblies are single-phase or double-phase, the resulting net biasexhibited is conventional (i.e., it behaves as a positive rate springwith which the bias force decreases as the travel distance (“stroke”) ofthe biased side of the transducer increases). Stated otherwise, springpreload force at its highest when the actuator is in its neutral/stableor de-energized position.

The transducer assemblies optionally employed in the present inventionmay have any number of diaphragm layers held in a stacked configuration.The stacking may have a “serial” or “parallel” configuration or acombination of the two. FIGS. 3A and 3B illustrate profile models ofstacked serial and parallel transducer assemblies, respectively.

In FIG. 3A the profile shows individual transducers placed inalternating directions, i.e., every other transducer diaphragm is placedwith its concave (or convex) side facing in the same direction. Moreparticularly, six individual frustum-shaped diaphragms are employed inthree pairs of double-sided transducer assemblies 100 where theiradjacent frame structures ganged together. One side of the entireassembly is braced against a reference support 16. The purpose of suchan arrangement is to connect the output of the first actuator (itscap/disc) to the input of the second actuator (also its cap/disc) whileproviding clearance for the relative movement of their outer frames.With each additional transducer pair 100, and without increasing theforce needed (i.e., keeping it constant), the overall or total strokepotential increases by a factor of 1 in the biased direction indicatedby arrow 103.

In FIG. 3B, the profile model of a parallel-configured transducerassembly is illustrated where the frustum diaphragms on one side 102 ofthe assembly are stacked in one direction (i.e., nested) and the frustumdiaphragms on the other side 104 of the assembly are stacked or nestedin the opposing direction. Sides 102 and 104 are coupled together viathe interface 106 between the innermost (facing) transducer diaphragmswith the stacked frame structure of one side 104 being braced againstreference plane 16. Such a construction amplifies the force potential ofthe transducer system in the direction of arrow 105 while maintainingthe same stroke as one pair. With each additional transducer pair (whereone of the pair is added to each side 102, 104), and without changingthe stroke of the system (i.e., keeping it constant), the total forcepotential increases by a factor of 1 in the biased direction indicatedby arrow 103.

FIG. 6 illustrates a configuration of a serially stacked single-frustumtransducer assembly 50 that may be employed with biasing according tothe present invention. Here, the diaphragms 54, 55 are coupled to eachother by way of frame 52 with their concave sides facing inward towardseach other. One of the capping structures 56 is fixed or mounted(reference plane) while the other 58 is not, thereby providing asingle-phase actuator where the “free” capping structure 58 translatestwice the distance (stroke) in the biased direction (as shown inphantom) as the capping structure would otherwise in a two-phaseactuator, and in which the outer frame assembly moves one-half thedistance of the top disc.

Another example of a possible construct of a parallel-stackeddouble-frustum transducer assembly that may be used in the presentinvention is illustrated in FIG. 7. Transducer assembly 90 comprisesmultiple double frustum transducer units having multiple diaphragmlayers 96, 98 on each side of the double-frustum structure with theirrespective capping members 100, 104 and frame sections 92, 94 ganged orstacked together. To accommodate the increased thickness of the device,additional frame sections or one or more spacer members or layers 102may be interposed between the transducer sides.

The relative force-stroke relationships of parallel and seriallyconstructed stacked transducers having conventional biasingcharacteristics are illustrated in the graph of FIG. 8. Assuming thatthe diaphragm transducer pairs forming the stacked assemblies are eachconstructed to have its capped structure(s)/interfaced surface(s)displaced or biased 1.0 mm from the reference plane/support when in theneutral or inactive position (i.e., no force applied) and to require 1.0Newton of force to move the capped structure/interfaced surface to astable position (i.e., no displacement), line A reflects theforce-stroke relationship of a single-unit (one transducer pair)transducer assembly. In particular, the transducers are inactive atpoint A1 (actuator neutral/stable position) and activated at point A2(stable position of the spring). This force-stroke relationship applieswhether the conventionally-biased single-unit assembly is stacked in aparallel (FIG. 1) or series (FIG. 6) configuration. Lines B and Creflect the force-stroke relationship of serially stacked transducerassemblies having two and three pairs of transducers, respectively.Point B1 and C1 represent their respective neutral positions and pointsB2 and C2 represent their respective bias-member stable positions.Similarly, lines D and E reflect the force-stroke relationship ofparallel-stacked transducer assemblies having two and three pairs oftransducers, respectively, where points D1 and E1 represent theirrespective neutral positions and points D2 and E2 represent theirrespective bias-member stable positions. The various oppositely-directedlines and prime designations (i.e., A1′, B1′, C1′, D1′, E1′) areindicative of the force-stroke relationship of the transducers intwo-phase use. As mentioned previously, each additional transducer pairin the serially stacked configuration increases the stroke output of thetransducer assembly without increasing the required force, while eachadditional transducer pair in the parallel stacked configurationincreases the force output of the transducer assembly without requiringan increase in stroke.

The frustum transducers described thus far are pre-loaded/biased so asto exhibit force-stroke characteristics of a conventional or positiverate spring system, i.e., a system with a decreasing force bias enables.At least a component of such conventional biasing may be required oroptimum to obtain the desired performance or output characteristics, forexample, in use with a normally closed that requires a high initialpreload for sealing. However, for other applications, addition ofconstant force bias or negative rate spring bias component may bepreferred in order to improve valve adjustment range. In otherapplications, constant and/or negative rate spring biasing, alone, maybe preferred. Each of these types of systems is described below.

Referring now to FIG. 9, an example of a double frustum-shapedtransducer biased to perform according to a constant force model isillustrated. Transducer 60 includes EPAM™ film 70 held about itsperimeter by frame sections 64 which in turn is mounted to and spacedfrom a baffle wall 62. Frame support 66 separates frame sections 64,which collectively may be referred to as a frame. The upper one of thediaphragm's centrally positioned capping structure 68 has a central boreor slot 72 through which the constant-force spring 76 passes and isfixed to the grounding structure with a fastener head 74. The constantforce spring is rotatably mounted on a roller 78 fixed to a bracket. Theconstant force (zero-spring rate) spring, also called a “negator”spring, provides a more optimum bias than the conventional rate coilspring. This improved bias allows the actuator to do more force, stroke,work, and power.

Another variation of a constant force biased transducer system employs amass or weight positioned on a transducer's diaphragm. FIG. 10illustrates a transducer assembly 80 where the EPAM™ film 84 has beenbiased in a direction perpendicular to frame 82 by a simple weight 86attached to or formed integral with the cap section 88. A transducerdevice which is weight/mass biased will typically be position parallelrelative to the ground reference plane (i.e., lie flat) so that the pullof gravity on the weight 86 symmetrically biases the transducerdiaphragm 84 along a Z-axis.

While both examples offer constant (or at least substantially constant)rate biasing, the “spring” variation will sometimes be preferablebecause it can operate across a wide range of frequencies withoutsignificant consideration of inertial loads as inherent to a weightedbiasing approach. As such, it may be better suited to actuators or othertransducers in which reaction time is key and/or are intended to cycleat high frequencies.

Yet, in one mode of use, the weight/mass biased transducer 80 isespecially useful in a cyclic application. More specifically, such biasmember 86 may be employed to initially bias or preload diaphragm 84 in atransducer system configured to run within a given frequency range. Themass of the system may be weighted or tuned so as to offer maximumdisplacement at a desired frequency of operation, i.e., the frequency atwhich the diaphragm is caused to move. Ideally, when a constantoperating frequency can be employed, the size of the mass is selectedfor resonance by modeling the system as a mass-spring system ormass-spring-damper mechanical system. In variable frequencyapplications, the transducer may be designed so that the peakperformance range covers a broader section of frequencies, e.g., fromabout 0.1 to about 300 Hz. Such mass-tuned transducers are described ingreater detail in U.S. patent application Ser. No. 11/361,703,incorporated herein by reference.

In any case, the constant or substantially constant rate biasing aspectoffered by either one of the above spring types is advantageouslycombined with a positive or negative rate bias means as describedfurther below. In addition, it is to be understood that other constantor substantially constant rate bias members may be employed alone or insuch a fashion. A non-exhaustive listing of examples includes:pseudoelastic biasing members (e.g., as noted above) and high-volume airsprings.

Various negative rate spring-biased transducers are now described indetail with respect to FIGS. 11-14. In the transducer 110 shown in FIG.1, a leaf spring mechanism used to bias the diaphragm 114 in a directionperpendicular to frame 112. The leaf spring mechanism includes anelongated bowed member 118 (also simply referred to as a “leaf spring”)having slotted end members 124. The bowed member 118 is attached to capmember 116 by a bolt 122 and a nut (not shown) with its concave surfacefacing away from the diaphragm. While the orientation of the leaf springrelative to the diaphragm may be at any angle, a diagonal orientationallows use of the longest spring, and therefore, undergoes the leastamount of stress for the same amount of deflection. A spacer or boss 128is captured between leaf spring 118 and cap member 116. Linkage members.120, in the form of mounting bracket or legs, are affixed to frame 112by way of bolts 130 where the distal end of a bolt is aligned within acorresponding slot 126 in a leaf spring end 124. The linkage membersallow the necessary degree of freedom for axial displacement of bolt122. As leaf spring 118 bows in and out, linkage members 120 rock backand forth. The orientation can be any angle but a diagonal orientationallows use of the longest spring possible which undergoes the lowestamount of stress for the same amount of deflection.

When bow member is sufficiently long, the relation of the linkagemembers and the bow member causes buckling of the bow member. The degreeof buckling increases as the cap returns to the stable position of theactuator. Under such conditions, the net effect of the systemconfiguration results in the elongate member serving as a negative ratespring rather than as a common leaf spring as described above. Thisoccurs in an analogous fashion as in the structure described below.

FIG. 12 illustrates a spring element 160 that can be configured for useas a negative spring rate biasing member. Spring element 160 comprises anumber of fingers, petals or elongate members 162 which extend radiallyinward (at an angle) from the frame 164 to define (in this example) a“clover” shaped structure with a hole 166 where the petals may meet (buttypically are not joined). However, any number of petals may beemployed, most typically in a symmetrical configuration. The number ofpedals linearly affects the overall stiffness and spring rate of thestructure, i.e., the more pedals, the greater the overall stiffness andspring rate. Symmetry in the flexure arrangement creates a very stablecentered radial support without the additional friction and complexityof sliding, rocking or rolling elements in an assembled system whenemployed in a transducer assembly.

The spring element itself may be stamped, punched, laser cut, etc. fromany conventional elastic spring material including polymers, fiberglass,glass-filled polymer, carbon steel, stainless steel, titanium, etc. Whenthis is the case, it will perform substantially as represented below.

FIGS. 13A and 13B illustrate a transducer 180 incorporating springelement 160. Here, the inwardly extending petals or fingers 162,extending from frame 164 are secured to produce a curved, S-shaped orbowed configuration. Specifically, each elongate member 162 has a baseflexure portion 196 and an end flexure portion 198 with an outwardlycurved central portion 200 extending therebetween. The ends of thefingers are captured and held against capping member 184 by a centrallypositioned nut/bolt 192 or the like. A center disk 182 forces the endsof the fingers 162 a selected distance (larger than hole 166) from thebody of the bolt 192. A washer 188 covers some portion of the fingerends.

As such, the clover petals 162 are flexed inwardly into a buckling modeof compression. The compressive force acts along a shallow anglerelative to capping member 184. With high compression force, but withlittle mechanical advantage, diaphragm film 186 is nonetheless stretchedto form the frustum architecture. So with one part, the clover leafspring bias element provides a simple optimized bias spring and radialsupport for the output shaft.

By varying the center washer diameter, spring element thickness, numberof members, degree of preload compression/buckling, etc., a wide rangeof spring rates can be obtained. FIGS. 14A-14D illustrate suchtunability. Specifically, FIG. 14A illustrates different spring ratesgenerated by the same structure as a result of changing center disk 182and washer 188 size. FIG. 14B illustrates the force-stroke relationshipas a function of varying the included angle of the spring fingers 162.FIG. 14C illustrates the effect of adding more legs to the spring platestructure 160. FIG. 14D illustrates the effect of increasing springmember 162 thickness. As explained further below, negative spring ratesare offered by such a structure.

Negatively biased transducers of the present invention may also be usedin pairs to form double-frustum architectures. For example, FIG. 13Cillustrates a cross-section of a transducer assembly 202 which includestransducer 180, operatively coupled to another frustum transducer 204 bymeans of a body frame 206 (similar to the manner in which body frame 44of FIG. 5 is employed) to form a double-frustum structure with thetransducers' concave sides facing away from each other. Given that theclover spring shown is a bi-stable device, it can be used in a two-phaseconfiguration as illustrated.

The above-described negative biasing mechanism, although variouslyconfigured, function similarly in that the force (over an intendedworking range) that they each exert on the transducer diaphragmincreases as the transducer's electroactive film moves from an inactiveto a fully activated position. They behave and perform similarly toknown devices that exhibit inherent bi-stable function, such as keyboarddome switches, solenoids or snap-feel devices.

An understanding of the “negative rate spring” behavior referenced abovemay be appreciated through comparison to a Belleville Washer structuremodel. A feature-to-feature comparison is offered between thediagrammatic illustration of a “modified” Belleville Washer structure inFIG. 15A and the negatively biased transducer device 180 of FIGS. 13Aand 13B. A Belleville Washer is symbolically illustrated in terms of agenetic coil spring (positive rate spring) and other basic cooperativecomponents. More specifically, system 220 is defined by a coil spring396 pivotally fixed 397 at one end to a support structure 398 andpivotally fixed 399 at the other end to a linear bearing which islinearly translatable across the ground structure 400, defining a linearbearing surface 402. The so-called “stable” position(s) of the coilspring 396 is when it is at stable equilibrium, i.e., without anycompressive or tension forces exerted on it. As such, in system 220, thestable positions of the coil 396 occur when the linear bearing is at alocation along the linear bearing surface 402 at which no forces areexerted on the coil spring 396. In the illustrated system, there are twosuch stable positions (i.e., it is bi-stable), one on each side (leftand right) of the structural support pivot point 397 at which the coilspring is not under either compression or tension. When directly underthe pivot and subject to maximum compression, the system is also isunstable equilibrium. On either side, adjacent this point the force ofthe spring drives the system to its nearest stable equilibrium position.

With these principles in mind, the component-to-component comparisonillustrated in FIG. 15A between the analogous Belleville Washerstructure 220 to a negatively biased transducer 180 of the presentinvention is as follows: the structural support 398 of the Bellevillemodel corresponds to the transducer's frame 164, the coil spring 396corresponds to the curved portions of the clover spring flexurescollectively 162, the structural support pivot 397 corresponds to theouter flexure points collectively 196, the linear bearing pivot 399corresponds to the inner flexure points collectively 198, and the linearbearing surface 402 corresponds to the nut/bolt 192 means used to securethe flexure ends to the cap member.

The inventors have found that the clover leaf spring does in factfunction according to a negative rate spring/Belleville Washer model.This theoretical relationship is shown with reference to FIG. 15B, whichis a schematic representation of two opposing clover leaf flexures. Theflexures are once again schematically represented by two coil springs,each having one of their respective ends oppositely wall-mountedopposite each other and their respective “free” ends coupled together.

The following variables are represented by the illustrated model:

-   -   L is a spring length,    -   x is the horizontal component of the spring length L,    -   y is the vertical component of the spring length L,    -   F_(L) is the total net force applied to the spring when a load        is placed on it,    -   F_(x) is the horizontal component of F_(L),    -   F_(y) is the vertical component of F_(L),    -   L_(i) is the spring length without any load applied (F_(L)=0),    -   dL is the change in the spring length as a load is applied,    -   K is the spring constant, and    -   θ is the angle defined by the intersection of the spring length        L and the x axis.

The following relationships are defined by the model:tan θ=y/x; sin θ=y/LL=√{square root over (x ² +y ²)}dL=L _(i) −LF _(L) =Fx+FyAccording to Hooke's Law, the following relationship is known:F=K·s,where s is the displacement of the spring from its equilibrium positionwhen a force F is applied to it. The vertical component Fy of the totalload F_(L) applied to the spring is analogous to the preload force of anindividual clover spring flexure. Given the above relationships, solvingfor Fy involves the following equations:

F_(L) = K ⋅ dL F_(y) = sin  θ(K ⋅ dL) F_(y) = y/L ⋅ (K ⋅ dL)$F_{y} = {\frac{y}{\sqrt{x^{2} + y^{2}}} \cdot \left\lbrack {K\left( {L_{i} - \sqrt{x^{2} + y^{2}}} \right)} \right\rbrack}$$F_{y} = \frac{{yKL}_{i} - {yK}}{\sqrt{x^{2}} + y^{2}}$$F_{y} = {{{yK} \cdot \frac{L_{i}}{\sqrt{x^{2} + y^{2}}}} - 1}$Accordingly, the spring can be modeled as a mechanical system that ispredictable for the purpose of transducer design, or otherwise.

In another aspect of the invention, material selection is employed toproduce a bias spring with a desirable rate. Specifically, byconstructing a transducer with a superelastic SMA material, such asNiTi, leaf spring, clover type spring or a coil spring that issufficiently stressed (but not used in a buckling mode of compression asdescribed above), this single bias means it can offer a heavy initialpreload, followed by substantially zero-rate spring performances (like anegator spring) for the remainder of the transducer stroke. While notbehaving exactly as the stress-strain curve presented in FIG. 16 due tothe specific geometric factors of a given spring design, a relatedoutput force profile for the bias member can be generated. In such asystem, loading above the “yield” point “Y” produces stress-inducemartinsite that reverts to austenite with the stress is reduced (i.e.,when loading and unloading the spring, respectively). Fatigue lifeshould be considered when employing such a bias member. However, lowerfatigue life of such highly stressed elements may not pose a problem inlow-cycle applications, such as medical use disposables.

With the above principles in mind, the inventors have found that,depending on the transducer performance characteristics (i.e., workoutput, power output, force output, stroke distance, stroke frequency)desired, and the type of application in which an EPAM transducer is tobe used, the optimum type of bias and the bias rate employed may vary.As such, the present invention involves the selection of the bias typeand bias rate which is optimum for a given application. An understandingof the force-stroke relationships of the various bias types/ratesfacilitates the appropriate selection.

FIGS. 17A-17C graphically illustrate the force-stroke relationships ofbias mechanisms which provide a positive force bias, a constant forcebias and a negative force bias. In particular, the lines P and C of thegraph of FIG. 17A represent the force-stroke relationships,respectively, of positive force biasing and constant force biasing. Asrepresented by line P, with positive force biasing, the bias forcedecreases as the spring deflection, and thus the transducer diaphragmstroke distance, increases towards a more stable position. Asrepresented by line C, the force does not change throughout the springdeflection/stroke distance.

FIG. 17B illustrates the force-stoke relationship of negative forcebiasing, which is inherently bi-stable. Point A on the curve representsthe spring's first stable position in which it is fully spring-loadedwith no force yet applied to it and, thus, maximally displaced. Theportion of the curve between points A and B reflects the initial“buckling” of the spring in which the spring moves from its maximallydisplaced position, requiring a maximum amount of force required. PointB represents the first inflection point in which the spring's bias ratereverses directions, i.e., the maximum amount of force required fordeflection has been reached. The curve between points B and C reflectsthe fact that continued displacement of the spring requires less forceto achieve the first inflection point. Point C reflects the spring'sneutral position (unstable equilibrium position) in which it reaches aposition of no deflection (stroke=0) at which position no amount offorce is necessary to maintain this position. The curve between points Cand D reflects the necessary increase in force to continue the spring'sdeflection past the neutral position. Point D represents the secondinflection point in which the spring's bias rate once again reversesdirection. Continued deflection of the spring, reflected between pointsD and E, requires less force as it once again reaches its maximaldisplacement, but in the opposite direction). Point E on the curverepresents the spring's second stable position in which it is once againfully spring-loaded.

The advantage of a negative biasing over conventional (positive)biasing, at least in the context of transducer stroke distance, isreflected in FIG. 17C which charts the force-stroke curves oftransducers biased by a simple coil spring (see FIG. 4) and a cloverspring (see FIG. 14), respectively. As represented by line P, as thedisplacement/stroke distance of the device employing the coil springincreases, the available output force decreases significantly. Asrepresented by line N, as the displacement/stroke distance of the deviceemploying the clover spring increases, it takes significantly less forceto achieve a greater stroke distance. For example, the coilspring-biased device, at about 0.15 N of force produces a strokedistance of about 0.25 mm; whereas, at that same force, the cloverspring-biased device produces a stroke distance of about 1.0 mm, 4 timesthat of the coil spring.

FIG. 18 presents a bar graph illustrating the relative strokecharacteristics of various single-phase frustum transducers, each beingbiased by a different type of bias mechanism: coil spring biased (FIG.4), film-biased double frustum diaphragm (FIG. 5), constant forcemechanism (FIGS. 9, 10) and a negative spring mechanism (FIGS. 11-14).The transducers were constructed to eliminate certain variabilities(e.g., film thickness and layer count) amongst them, and operated at thesame DC voltage and as close as possible force (i.e., about 0.5N andabout 2.5kv). As illustrated in the bar graph of FIG. 18, the transducerhaving a diaphragm subject to a negative rate bias (transducer D)achieved a maximum stroke distance far greater than each of the others(from about 2.5× to about 5×), where transducer A was biased by the coilspring, transducer B was biased by an opposing frustum diaphragm, andtransducer C was biased by a constant force mechanism.

Furthermore, as illustrated in the graph of FIG. 19, negative biasedtransducers (represented by line N) operate within far greater thresholdvoltages (i.e., the voltage at which there is substantially nocorresponding increase in stroke distance) than do comparabletransducers biased by positive rate and constant force mechanisms(represented by lines P and C, respectively). Additionally, as shown inFIG. 20, negative biased transducers also advantageously produce a lowerelectric field (N/C) than do comparable positive biased transducers atthe same operating voltage.

Another advantage of negatively biased devices of the present inventionis that they are inherently bi-stable. As evidenced by the graph of FIG.17B and discussed above, negatively biased transducers having a singlefrustum structure (as illustrated in FIG. 14) can therefore be employedin two-phases to deliver output (or receive input) in two differentdirections. In physical terms, points B and D define the end points(i.e., commencement and termination) of the buckling or “snap”experienced by the biasing structure (equivalent to the “snap” undergoneby a keyboard dome switch, for example). The portion of the curvebetween points A and B can be controlled by matching the diaphragm'sfilm stiffness/thickness and the preload applied to the diaphragm. Inother words, the film stiffness can be selected (or is inherently) suchthat the spring coupled to the film does not move into this region.

This is evidenced in FIG. 21 which illustrates the force-strokerelationships of a selection of frustum-shaped, negative biasedtransducers having varying film thicknesses and varying preload/biasangles (i.e., the angle that the uncapped portion of the diaphragm makeswith the plane defined by the transducer frame (angle α in FIG. 2B).

The transducers (A-D) in the experiment conducted had the following filmthicknesses and bias angles: A: 0.010″, 20°; B: 0.010″, 25°; C: 0.015″,25°; D: 0.020″, 25°. From the plotted force-stroke results, thefollowing observations can be made: (i) with these variations inthickness and bias angle, there was virtually no difference in theinitial diaphragm disc height amongst the transducers; (ii) the totalstroke distance is more dependent upon bias angle and less dependentupon film thickness; (iii) the force necessary for the transducerdiaphragms to achieve the stable positions is more dependent on filmthickness and less dependent upon bias angle; and (iv) negative biased(as well as positive and constant force biased) transducers offer animmense degree in tunability (in output performance characteristics)while minimizing space and weight requirements.

As with the positive spring bias and constant spring bias transducers,the negative bias transducers of the present invention may be stacked tomodify the system's output force (i.e., spring constant) or the strokedistance (i.e., deflection). Stacking the frustum transducers in thesame direction (parallel stacking) increases the output force/springconstant with the same stroke/deflection. Stacking the transducers inalternating directions (series stacking) results in greater strokewithout changing the output force.

Selectively mixing and matching directions of the transducers allows aspecific output force and stroke capacity to be designed into a system.Additionally, for more complex applications, it may be desirable toemploy more than one type of bias with a transducer assembly. With theNiTi spring variations described above, such a result is achieved—ineffect—by a single bias member in transducer/bias member architecture asshown in any of FIGS. 4, 11, or 13A-13C, etc. (i.e., without bucklingthe leaf or “clover” spring members). Moreover, a transducer assemblymay have any combination of transducer architectures (e.g., singlefrustum, double frustum or both), stacking configurations (i.e., serialor parallel or both), and biasing mechanisms (e.g., positive, constant,negative or any combination thereof).

FIG. 22 illustrates the effect of combining a positive bias spring rate“P” (active/engaged over a portion of the length of transducer stork) incombination with a negative rate bias “N” (active/engaged over theentire length of transducer stroke) to yield a combined bias rate “C”.

Yet another biasing approach is illustrated in FIG. 23. Here, alinkage-based bias cartridge 300 is provided comprising a plurality ofsimple compression springs 302 carried by telescoping links 304 andconstrained by stops 306 between an outer frame 308 and central boss308. While the buckling/unbuckling beam variations of the negative biasspring 160 discussed above requires somewhat of an abstract comparisonto the Bellville Washer model, above, each quadrant of negative-ratebias 300 offers an essentially direct comparison.

While mechanically more complex than the buckled “clover spring”approach described above, the linkage device is advantageous for anumber of other reasons. Namely, it is very easily tuned. For example,its modularity allows for simple substitution of springs to achievedifferent overall rates. Free length of the springs can be increased ordecreased and/or preload on the spring can be increased or decreased.Such variation may be observed in comparing the cartridge configurations300′ and 300″ as shown in FIGS. 24A and 24B. Further variation forspring rate tuning/design is possible in connection with hub size,telescoping linkage length, stop position, frame size, linkage number,etc.

In addition, while some asymmetry in bi-stable performance may beinherent to buckling spring devices as shown in FIGS. 13A-13C (thoughthis can be addressed by using opposite-facing members in a “stack”) theoperation of linkage spring assembly 300 is naturally symmetrical solong as symmetrical frame components are employed. FIG. 25A illustratesthe exemplary negative rate performance of a cartridge spring assembly300 as shown in its various stages of 2-phase actuation in FIG. 25B.

Yet another advantage is the ease with which a spring cartridge assembly300 is in integrated into an actuator assembly as simply one more layerof a double-frustum stack. An example of such an assembly is shown inFIG. 26. Together with appropriate fasteners and spacers 310, biascartridge 300 is joined to a pair of frustum-type EPAM transducercartridges 312. The overall transducer assembly 314 produced is adouble-frustum EPAM transducer incorporating a bias cartridge. FIG. 27illustrates the comparative performance of transducer assembly 314(labeled, “inverted double diaphragm with linkage spring”) as comparedto a “simple” transducer 30 (labeled, “double diaphragm”) as shown inFIG. 5. The performance enhancement is dramatic in terms of availablestroke, thus, work output or power potential.

FIG. 28A is a perspective view of a“planar” type of lineartransducer/actuator 320 including a lateral input/output type ofnegative spring rate “cartridge” bias assembly 322. In such a device,lateral movement of the EPAM material 324 in connection with interfacemember 326 causes translation of output rod 328. Absent the includednegative rate bias cartridge 322, details of planar EPAM devices areavailable in the various references incorporated herein—above. Asillustrated in the assembly drawing view of FIG. 28A, transducer 320comprises, together with appropriate fasteners, bias cartridge 322joined to a pair of planar EPAM transducer cartridges 330. FIG. 29A-Cillustrates the negative bias assembly 322 shown in FIGS. 28A and 28B inthree stages of its potential two-phase actuation cycle (correspondingto the In/Out/Neutral positions respectively, as illustrated in FIGS.29A, 29C and 29B of the output rod 222 labeled on the drawing).

As with the out-of-plane actuated negative spring cartridge 300,in-plane negative spring bias cartridge 322 is highly variable inconfiguration for tunable output. Still, it is to be appreciated thatsignificant modifications can be made to the structures withoutdeparting from the spirit of the invention. For example, hub 310 can beminimized or eliminated, pivoting hinges can be replaced with livinghinges or ball joints, frame 308 may be integrated with an EPAMcartridge frame, etc.

FIGS. 30A and 30B illustrate two exemplary applications in which atnegative rate clover leaf flexures are employed. Both applicationsinvolve fluidic control mechanisms 248, 250 in which the opening andclosing of valve inlet and outlets are controlled with the transducers.The valves each include a housing which may be a two-piece structure forease of manufacture in which top and bottom housing portions 252 a, 252b are secured together subsequent to constructing the interiorcomponents of the valves. Extending from a top surface of top housing252 a is a fluid outlet conduit 264 having a fluid outlet lumen 262which is in fluid communication within an upper portion 272 a of aninterior chamber within the top portion of the valve at outlet orifice276. Similarly, extending from the bottom surface of bottom housingportion 252 b is a fluid inlet conduit 260 having a fluid inlet lumen258 (i.e., liquid, gas, vapors, etc.) which is in fluid communicationwithin a lower portion 272 b of the valve chamber at inlet orifice 278.The upper and lower portions of the fluid chamber are in fluidcommunication with each other by way of one or more openings (not shown)within capping member 270. As illustrated, the housing portions andconduits may be held together in any suitable manner, including by wayof threaded surfaces and mating nut components 256 a, 256 b.Alternatively, the housing and conduits may be integrally fabricatedinto a monolithic structure by molding techniques or the like.

The respective transducer portions of valves 248, 250 each includes asingle-frustum, double-phase transducer component mounted to the valvehousing within fluid chamber 272. Specifically, the transducercomponents each include an EPAM diaphragm 268 stretched within a frame288 and a cap portion 270 centrally attached to the diaphragm. Frame 288is sandwiched between the top and bottom portions 252 a, 252 b of thevalve housing such that the cap portion is positioned generallyperpendicular to the luminal axes of the fluid inlet and outlet conduits260, 264. Specifically, in the illustrated embodiments, frame 288 isheld between a spacer member 266 b and bottom housing portion 252 b.

An inlet sealing member 280, which in these embodiments is a screw head,is positioned on the underside of capping member 270. The screw's stemextends through and from the top side of cap member 270 and is heldfixed to the cap member by a nut 294 threaded to the screw's stem 286.Positioned at the distal end of screw stem 286 is an outlet sealingmember or valve seat 274. Both sealing members 274, 280 are configuredto seal respective opposing orifices 276, 278 when in contact therewith.For example, to facilitate sealing, the screw head may be covered by orbe made entirely of a compliant polymer material.

In both valve embodiments 248, 250, a clover buckled spring is providedon the top side of capping member 270. The spring flexures 284 arepositioned so as to provide a negative-rate, downward force on capmember 270 towards inlet opening 278. The free or outward-extending ends292 of the flexures are held fixed between the two housing portions;specifically between another spacer 266 a and top housing portion 252 a.As such, the two spacers 266 a, 266 b in each of the embodiments arestacked and interposed with the flexures and diaphragm frame to maintaina selected spacing between them. The inwardly extending ends of flexures284 are joined (if not made from a single piece) together and capturedor held between a nut 296 threadedly engaged with screw stem 286 andoutlet valve seat 274.

While the valve components described thus far are substantially the samefor both valves 248, 250, other components and features of therespective valves are provided which differentiate the biasing of theirtransducers. Unlike valve 250, valve 248 further includes a conventionalor positive-rate coil spring 282 interposed between the capping member270 and the interior wall 290 of bottom housing 252 b. Coil spring 282acts to pre-load or bias diaphragm 268 and cap member 270 to better sealopening 278. The combination of springs offers the blocking force of acoil spring bias with the overall stroke seen in a negative spring ratebiased structure. In another example (not shown), similar (albeit lessdramatic) advantages are offered by combining a positive-rate coilspring with a negator spring or weight bias.

In fact, a very similar performance profile can be achieved by employinga spring (e.g., a coil spring or leaf spring) comprising superelasticNiTi as discussed above. Without further geometric manipulation (e.g.,as with the buckled/buckling springs employed in the embodimentsdiscussed above), the spring rate will roughly parallel the materialsnatural stress stain performance shown in FIG. 16 to offer a spring thatfirst compresses with a positive rate, then at a substantially flatrate.

With valve 250, on the other hand, the transducer diaphragm ispre-loaded by way of the “pulling” force exerted on it by couplingcapping member 270 to the clover leaf spring. This coupling isaccomplished by a plate member 298 attached to nut 294 and extendingover and contacting the outwardly flexed portions of the flexures 284.Plate 298 provides a buttressing surface against which the flexuresexert a force which is in turn translated to capping member 270 via nut294 and screw stem 286. In such a valve, the bias preload can beconfigured such that the valve is either naturally/normally open orclosed.

In yet another application, a molded diaphragm negative rate bias memberis provided. FIG. 30C shows a valve assembly 350 comprising inlet andoutlet ports 352, 354—respectively—received within a valve body orhousing 356. An EPAM frustum-type actuator 358 is covered by an actuatorcap 360 joined to the valve body. In the valve 350, position of valvepoppet 362 is controlled by actuator 358. The actuator is biased, andvalve chamber 362 closed by bias diaphragm 364. As such, in thisvariation, the negative-rate bias member (bias diaphragm 362) servesdual-duty as a bias spring and baffle wall within the valve body.

FIG. 31 shows a pump assembly 370 biased in the manner of the valvetransducer in FIG. 30C. Specifically, assembly 370 comprises inlet andoutlet ports 372, 374—respectively—received within a pump body orhousing 376. An EPAM frustum-type actuator 378 is covered by aprotective actuator cap 380 joined to the pump body. The actuator drivespump piston 382 and is biased by bias diaphragm 384. Bias diaphragm 384also completes pump chamber 386 in communication with check valves 388.

FIG. 32 illustrates the spring rate of molded rubber biased diaphragm364/384. In this example, the part is molded in NITRILE rubber. Otherpotential materials for molding the piece include, but are not limitedto SILICONE, Neoprene®, Epichlorohydrin, Fluorosilicone, Viton® andPropylene. FIG. 33 illustrates the measured performance of a moldeddiaphragm negative spring over a selected region of travel. Thisexperimental output curve is in substantial agreement with thetheoretical discussion of negative rate springs discussed above.

The final application of a negative rate spring biased transducerdiscussed herein (though a myriad of other application are possible) isshown in FIG. 34. Here, a lens positioner/focus assembly 380 is provedthat employs a transducer negatively biased by a molded spring element382. In general terms, assembly 380 further comprises a lens 384, anEPAM actuator 386, a top housing 388, a lens barrel 390, an alignmentbushing/housing 392, and finally a CCD chip 394 to capture images.

FIG. 35 illustrates the relative performance of a device as shown inFIG. 34 (curve 396) as compared to a coil-spring biased device employedin the same application (curve 398). As expected of a negative-ratebiased spring actuator according to the present invention, improvedoverall stroke and more stroke at lower voltage is available.

As for other applications, it is also contemplated that the biasingapproaches disclosed herein may be employed in systems which provide formulti-angle/axis sensing or actuation. This is effected by providing adiaphragm, for example, with three independently addressable zones orphases having different stiffness/flexibility which, when activated,will expand differently causing the capping member to tilt on an angle.In a frustum-style actuators such a multi-phase device can providemulti-directional tilt as well as translation depending on the manner ofcontrol.

Based on the above, it should be apparent that any number of parametersof the subject transducers can be varied to suit a given application. Anon-exhaustive list includes: the type, rate and extent of biasing orpreload placed on an EPAM film; the amount of prestrain on the film(magnitude, angle or direction, etc.); film type (silicone, acrylic,polyurethane, etc.); film thickness; active vs. non-active layers;number of layers; number of film cartridges; number of phases; thenumber of transducers; the manner of stacking, etc. For example, the oneor more spring rates of the transducers/transducer assemblies may beselected and adjusted by bias type, construct, spring constant, forcerate, diaphragm film thickness, frame construct, diaphragm filmmaterial, etc. to achieve the performance characteristics desired.

The constituent transducer components may be bonded together using anyviable technique such as adhesives, thermal bonding, friction welding,ultrasonic welding, or be mechanically locked or clamped together.Regardless of the configuration selected for the subject transducers,various manufacturing techniques are advantageously employed.Specifically, it is useful to employ mask fixtures (not shown) toaccurately locate masks for patterning electrodes for batchconstruction. Furthermore, it is useful to employ assembly fixtures (notshown) to accurately locate multiple parts for batch construction. Otherdetails regarding manufacture may be appreciated in connection with theabove-referenced patents and publication as well as generally know orappreciated by those with skill in the art.

Methods associated with the subject devices are contemplated in whichthose methods are carried out with EPAM™ actuators. The methods may beperformed using the subject devices or by other means. The methods mayall comprise the act of providing a suitable transducer device. Suchprovision may be performed by the end user. In other words, the“providing” (e.g., a pump, valve, reflector, etc.) merely requires theend user obtain, access, approach, position, set-up, activate, power-upor otherwise act to provide the requisite device in the subject method.

Regarding methodology, the subject methods may include each of themechanical activities associated with use of the devices described aswell as electrical activity. As such, methodology implicit to the use ofthe devices described forms part of the invention. The methods may focuson design or manufacture of such devices. In other methods, the variousacts of mechanical actuation are considered; in still others, the powerprofiles, monitoring of power and other aspects of power control areconsidered. Likewise, electrical hardware and/or software control andpower supplies adapted by such means (or otherwise) to effect themethods form part of the present invention.

Yet another aspect of the invention includes kits having any combinationof devices described herein—whether provided in packaged combination orassembled by a technician for operating use, instructions for use, etc.A kit may include any number of transducers according to the presentinvention. A kit may include various other components for use with thetransducers including mechanical or electrical connectors, powersupplies, etc. The subject kits may also include written instructionsfor use of the devices or their assembly. Such instructions may beprinted on a substrate, such as paper or plastic, etc. As such, theinstructions may be present in the kits as a package insert, in thelabeling of the container of the kit or components thereof (i.e.,associated with the packaging or sub-packaging) etc. In otherembodiments, the instructions are present as an electronic storage datafile present on a suitable computer readable storage medium, e.g.,CD-ROM, diskette, etc. In yet other embodiments, the actual instructionsare not present in the kit, but means for obtaining the instructionsfrom a remote source, e.g. via the Internet, are provided. An example ofthis embodiment is a kit that includes a web address where theinstructions can be viewed and/or from which the instructions can bedownloaded. As with the instructions, this means for obtaining theinstructions is recorded on suitable media.

As for other details of the present invention, materials and alternaterelated configurations may be employed as within the level of those withskill in the relevant art. The same may hold true with respect tomethod-based aspects of the invention in terms of additional acts ascommonly or logically employed. In addition, though the invention hasbeen described in reference to several examples, optionallyincorporating various features, the invention is not to be limited tothat which is described or indicated as contemplated with respect toeach variation of the invention. Various changes may be made to theinvention described and equivalents (whether recited herein or notincluded for the sake of some brevity) may be substituted withoutdeparting from the true spirit and scope of the invention. Any number ofthe individual parts or subassemblies shown may be integrated in theirdesign. Such changes or others may be undertaken or guided by theprinciples of design for assembly.

Also, it is contemplated that any optional feature of the inventivevariations described may be set forth and claimed independently, or incombination with any one or more of the features described herein.Reference to a singular item, includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said,” and “the”include plural referents unless the specifically stated otherwise. Inother words, use of the articles allow for “at least one” of the subjectitem in the description above as well as the claims below. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Without the use of such exclusive terminology, the term“comprising” in the claims shall allow for the inclusion of anyadditional element—irrespective of whether a given number of elementsare enumerated in the claim, or the addition of a feature could beregarded as transforming the nature of an element set forth n theclaims. For example, adding a fastener or boss, complex surface geometryor another feature to a “diaphragm” as presented in the claims shall notavoid the claim term from reading on accused structure. Statedotherwise, unless specifically defined herein, all technical andscientific terms used herein are to be given as broad a commonlyunderstood meaning as possible while maintaining claim validity.

In all, the breadth of the present invention is not to be limited by theexamples provided. That being said, we claim:

1. A transducer assembly comprising an electroactive polymer and atleast one biasing element, the improvement consisting of at least onebiasing element set to provide a negative spring rate within thetransducer assembly.
 2. The transducer assembly of claim 1, furthercomprising at least one other biasing element set to provide a positivespring rate.
 3. The transducer assembly of claim 1, wherein the at leastone biasing element comprises any of a coil spring, leaf spring, airpressure, fluid pressure or a combination thereof.
 4. The transducerassembly of claim 1, comprising a plurality of biasing elements in theform of leaf springs arranged in a clover configuration.
 5. A transducerassembly comprising electroactive polymer and a positive, rate biasingelement, the improvement consisting of at least one biasing element setto provide a negative or substantially zero spring rate.
 6. A diaphragmtransducer assembly comprising electroactive polymer and at least onebiasing element, the improvement consisting the at least one biasingelement having a bistable configuration to allow the transducer toactuate in opposite directions without further biasing.
 7. Thetransducer assembly of claim 6, wherein the diaphragm includes a cap toform a frustum-style assembly.
 8. The transducer assembly of claim 1,wherein the transducer assembly forms part of a lens positioner, a valvemechanism, a pump, a light reflector, a speaker, a vibrator, a hapticfeedback device or a force feedback device.
 9. A negative spring rateassembly comprising: a compressible member configured to be in a mostcompressed condition when the assembly is in a neutral position and in aleast compressed condition when the assembly is in an extended position;and an output member associated with the compressible member, whereinthe output member is leveraged most when the assembly is in the neutralposition and is leveraged least when the assembly is in the extendedposition.
 10. The assembly of claim 9, further comprising a frameassociated with the compressible member wherein output force of theoutput member is substantially perpendicular to the frame.
 11. Theassembly of claim 9, further comprising a frame associated with thecompressible member wherein output force is along a line parallel to theframe.
 12. The assembly of claim 9, the compressible member comprises aC or S shaped section of material.
 13. The assembly of claim 12, whereinthe compressible member comprises a buckled elongate form.
 14. Theassembly of claim 9, wherein the compressible member comprises aplurality of coil spring and the coil springs are each mounted on alinkage arm, the linkage arms rotatably connected a central hub, the hubproviding the output interface.
 15. A transducer assembly comprising: amolded negative race spring diaphragm and electroactive polymer, eachcoupled to a frame, wherein the electroactive polymer is configured in afrustum shape and wherein the negative rate spring diaphragm isoperatively coupled to the electroactive polymer to provide biasing. 16.The transducer assembly of claim 15, further comprising a lens locatedsubstantially at a center of the electroactive polymer frustum.
 17. Thetransducer assembly of claim 15, further comprising valve popett locatedopposite a valve inlet or outlet conduit in a valve body, wherein thespring diaphragm defines a portion of a valve chamber.
 18. Thetransducer assembly of claim 15, further comprising a piston region,substantially at a center of the electroactive polymer frustum, andcheck valves for inlet and outlet conduits in a pump body, wherein thespring diaphragm defines a portion of a valve chamber.
 19. The assemblyof claim 9, wherein the compressible member comprises a spring element.20. The assembly of claim 9, wherein the output member comprises one ofa frame, cap structure, linkage and a shaft.